The market for metal containers has developed widely in recent years due in part to the introduction of the easy open end. While the easy opening feature has been shown to be both effective and convenient, it has given rise to a collateral problem of littering, since traditionally the easy opening feature was pulled free from the container to expose the contents and then subsequently discarded. The indiscriminate disposal of the pull tabs is not only unsightly, but can also present a safety hazard particularly on beaches and in parks. Further, the relatively small size of the separated tab presents a challenge to those concerned with the collection and recycling of waste material. The solution to this problem resides in a nondetachable tab and preferably a tab which is compatible with the end closure and is recyclable.
While the industry has addressed this problem by developing a number of closure structures, one of the more successful has been a can end which employs a retained lever tab. In this structure, the tab is joined to the container end by a tongue or flap which is lanced in the web of the tab, and which serves as a hinge or connecting strip. Typically, the tip of the tongue is apertured and staked to end by means of an integral rivet. Since the tab functions by levering open a scored portion of the end panel, it must be sufficiently rigid to prevent distortion of the curled rim when leverage is applied to the lift end of the tab to effect rupture and displacement of the scored panel. At the same time, the tongue of the tab must be sufficiently bendable to permit the user to open the container and subsequently bend the tab back out of the way into a position of repose. The situation is aggravated by the user's inclination to fatigue the tab by bending it back and forth in an effort to free the tab from the container in accordance with past practice.
Typically, tab rigidity is provided by utilizing heavy aluminum tab stock and by curling the edges of the stock to form a tab rim. Such a structure, however, results in a tab tongue which lacks bendability and is prone to fracture when subjected to severe bending, as may be encountered when it is pivoted forward to open the end and then subsequently bent backward to fold the tab out of the way. Fracture of the tongue generally occurs between the terminal ends of the lance and the rivet hole or tongue aperture.
This lack of bendability of the tab tongue can be overcome in part by a more elaborate tab structure, wherein a retaining strip of plastic or ductile aluminum is interleafed into the folds of the tab nose, thereby providing a flexibility and fracture resistance linkage between the tab and the end. Such a structure requires a premium tie strip and appreciable press time for fabrication.
Alternative structures have been proposed using a soft ductile alloy for the tab, but with a more complex configuration as a means for achieving rigidity. In another instance, tin-plated steel has been suggested as a material of construction.
The problems of material recycling and raw edge corrosion or alternatively of increased manufacturing cost, which are attendent with these structures, are not readily resolved.
Typical of the prior art in connection with this type of invention are the Radtke U.S. Pat. No. 4,210,257 and the LangsederU.S. Pat. No. 4,211,335.
Accordingly, it is the primary objective of the instant invention to provide a lever tab structure for an easy open end which is sufficiently rigid to operate effectively without distorting, but where the tongue is sufficiently bendable so that it resists fracture and separation from the end despite repeated bending and rebending.
It is further an objective of the instant invention to provide a nondetachable tab structure which does not require a retaining strip and which is simple and economical to manufacture.
Finally, it is an objective of the instant invention to provide a tab structure which is compatible with the can end closure, thereby facilitating material recycling and minimizing corrosion.